There has been widely used an electric actuator such as a motor and a solenoid in order to convert an electrical signal into mechanical movement or hydraulic pressure with the increase in electronic control of various controlled objects. On the other hand, when an electric actuator is used for control that involves human life such as control in a motor vehicle, the electric actuator is required to have high reliability.
In order to improve reliability of an electric actuator, it is necessary to reliably detect failure of a current control device which is used in the electric actuator, and then, depending on the type of the detected failure, perform a fail-stop function for stopping the failed current control device so as to prevent an unsafe state of a host system, or a fail-operative function for continuing current control while avoiding the use of a failure part when the current control is possible.
As a current control device that detects failure of a current detection circuit whose failure is difficult to be detected, there is known one that detects failure of a current detection circuit by using the output of a motor rotation speed sensor in addition to the output of the current detection circuit (see PTL 1, for example).